Re: Vector type (Re: challenging constraint situation - how do I make it)

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Alban Hertroys <alban(at)magproductions(dot)nl> writes:
> Tom Lane wrote:
>> Except that what you want is to forbid overlap, not forbid equality.
>> This is not possible with btree-based unique indexes, because btree
>> will not like an opclass whose "equality" member is not transitive.

> With what I have in mind, both overlap and equality would violate the 
> unique constraint. I don't quite see why someone'd want to forbid 
> overlap but to allow equality; isn't not allowing equality the whole 
> point of a unique constraint?

You're missing the point.  Letting "~" represent the operator that
tests for interval-overlap, we can have
	A	--------------
	B	       ------------------
	C	                   ----------------
so that A ~ B and B ~ C but not A ~ C.  This is too much unlike normal
equality for a btree to work with "~" as the "equality" operator.

			regards, tom lane